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Need Help Related to Rotational Inertia

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BigBad

Mon Feb 25 2013, 02:04PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

I'm wondering whether you should test it suspended in space with a bit of slack, but not too much to let you get into problems. That would avoid the problems with crashing, and also avoid the transition from ground effect. When you've mastered that, lower it closer to the ground, and then finally take off from the ground.

Patrick

Mon Feb 25 2013, 07:04PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Dr. Slack wrote ...

Ah, we've been ignoring the most complicated part of the overall control loop!

Google for 'pilot induced oscillation'

No need for google, ive studied that "phrase" for 10+ years, i was hoping youd have the decency not to mention it though.

(clearly ive been contributing, the brass and PID changes proove that now)

Steve Conner wrote ...

If you think you might be part of the problem, try to use only half as much control effort as you think you ought to. Eg, if you want to pull the stick all the way back, just pull it halfway.

yes, but when its your 3 year, 2k$ machine waffling about its hard to resist those temtations to "over-control" the machine, i see now how human test pilots can get killed...

BigBad wrote ...

I'm wondering whether you should test it suspended in space with a bit of slack, but not too much to let you get into problems. That would avoid the problems with crashing, and also avoid the transition from ground effect. When you've mastered that, lower it closer to the ground, and then finally take off from the ground.

Yes, i was thinking of the deep ocean type fishing line, and hanging the machine from the cieling...

Night flights conducted:

Seen above, bad stall again, did not retard throttle, forward speed high, then pitch back induced nose stall.

Better flight...

Steve Conner

Tue Feb 26 2013, 10:23AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

See 0:54 here. :-o

interesting to see that the copter has a little tail fin pitched at a very steep angle. Seems to me like this would counteract the pitching problem you have. The lift force from it would pitch down whichever end of the craft is travelling forwards, and the drag would provide some pitch damping.

Patrick

Tue Feb 26 2013, 07:43PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Steve Conner wrote ...

See 0:54 here. :-o

Your first vid showsthe 1998 crash, if i remember right, where both marine pilots were killed. I beleive this was a Power boost electrical/computer induced problem.

your second vid, shows copterritchies' machine (aka rimshotcopter) who has been helping enormously my bicopter efforts, and yes, i did come to your same conclusions about his tail fin...

I must continue testing, but it does look like after copterritchies advice, bad code has caused the entire problem!

Patrick

Thu Feb 28 2013, 05:33AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

heres important pics, :

Patrick

Fri Mar 01 2013, 04:43AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Huge breakthorgh!

in the above scematic pic with force locations, the CL and CG are right and shown right, but the flaw in my great effort may behaving mass to far out on the nose and tail. 1kg on a pivoting arm of 1m length, has a higher energy moment, compared to the same angular displacement of 1kg at 0.3m.

instead of changing the CG, which isnt nessacary, i need to concentrate the mass near the CG/CL, to reduce teh rotational inertia required to change any given pitch attitude! the mass as it was, was equally dispersed throughout the airframe.

BigBad

Mon Mar 04 2013, 04:54PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

Pretty sure that the CofG and CofL should be as close together as humanly possible. I don't see that you can gain anything by moving them apart.

Patrick

Mon Mar 04 2013, 07:32PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

[quote]
Pretty sure that the CofG and CofL should be as close together as humanly possible. I don't see that you can gain anything by moving them apart.

[/quote1362425373

but will any change in thrust cuase a attitude change thats predictable?

Also, i flipped the prop directions, and its behaving much better. even though as a stated previuosly i had them right (and did).

Patrick

Wed Mar 06 2013, 09:09PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

appaerntly this pic shows that my vertical CG was to close to the CL (about .7 inches)

this pic and other bicopter-ists have 3-4 inches between thier rotor disc and CG (vertically) this would seem to cuase a anti torque, to oppose my unwanted nose stall!

Ash Small

Thu Mar 07 2013, 01:21AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

other bicopter-ists have 3-4 inches between thier rotor disc and CG (vertically) this would seem to cuase a anti torque, to oppose my unwanted nose stall!

It certainly would help. I nearly suggested hanging a weight underneath, but this is obviously not the best solution (unless it's the battery pack, and you also devise a means of jettisoning one, and picking up another while underway)

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